Finally, we
have not been lucky this austral winter. On 21 May, there was a huge storm,
with hourly averages of wind speed up to 27 m/s and 6-min-peaks up to 38 m/s.
In the course of this storm, the communication link to the stationwas
interrupted and could not be restored (if the storm has been the cause can’t be
confirmed, however). Also other satellite communication means did not work
anymore, indicating that the station had also lost power. The reasons are not
clear (as there is no communication link to explore…). So, this means that
everything is now in ‘freezing’ mode. Inside the station and in the scientific
shelters, there should be no issue for the instruments – it should be dry and
relatively ‘warm’. However, the power outage means also that there is quite a
lot of maintenance work to be done when the next BELARE campaign starts in
November this year. In particular, the instruments which are installed on the
roof of PE station have to be checked in detail. Last year, when everything operated
without interruption during winter, it was much less maintenance work. We also
hope that the instruments have not encountered damage during that huge storm,
and also that the long time they will be now outside without being powered will
not lead to damage. Only by mid-November, when the first team arrives at PE, we
will know more details. Until then, we hope the best.
In the meantime, there is some time to go ahead
with some data analysis. Below, a graph for the monthly means of the total
particle number concentration is given, for all years/months available up to
now. There are several striking points : a) there is a clear yearly cycle,
with relatively high numbers during
summer and lower particle numbers during winter, b) winter numbers (May, June,
July) are extremely low (down to some tens of particles per cm3), c)
as soon as sunlight returns in spring (Sep, Oct), numbers go up distinctly, d) monthly
numbers are well repeated each year, however with some annual variation, e)
especially from November throughout March, the statistical means come with very
high standard deviations. Some explanations : during the summer months,
transport of air masses from lower latitudes or the coast to PE station is more
often than during winter when the strong atmospheric circular circulation
around Antarctica (polar vortex) is forming a quasi- barrier for this kind of
transport. In addition, there is also (almost) no sunlight which could trigger particle
formation processes by atmospheric photochemistry. In September, October,
sunlight returns, and also the polar vortex is becoming less stable, setting
the scene for atmospheric particle formation and transport. The high standard
deviations were caused by short-termed events (some hours to one day), during
which the particle number increased from 200/300 per cm3 up to 6000 per cm3.
Such events can be linked to either entrainment from the free troposphere
and/or the passage of clouds with or without precipitation.
